1. Field of the Invention
The invention relates to a metal implant which is corrosion resistant in the body.
2. Prior Art
An implant constructed of a metal, such as, titanium, tantalum or niobium, which is corrosion resistant in the body and consists essentially of (a) a leaf-shaped part to be inserted into the jaw bone, (b) a post-like part leading from the jaw bone through the mucous membrane into the mouth cavity, and (c) means for attaching the crown, bridge or some other superstructure, provided at the end of the post-like part pointing into the mouth cavity, is known.
Such implants have recently been described in German OS No. 2,853,638. Such leaf implants have previously preferably been inserted in the lateral tooth area for the attachment of total or partial tooth protheses in jaw bones. The rate of success for such implants, i.e., their staying time in the jaw until the necessity for removal of such implants, amounts up to about 50 percent after five years. This high loss-rate rests essentially on the cooperation of two factors, the negative influences of which reinforce each other. For one thing, implants of such prior form are not surrounded directly by the bone tissue, but rather a close attachment of the bony tissue of such implants with a layer of soft tissue occurs, which separates the implants from the real bone bed. This occurs because the implants do not have sufficiently large surfaces, thereby not transferring the chewing forces in the form of a pure pressure load to the bone.
Therefore, relative movement between the adjacent tissues and the surface of the implant always occurs at the surfaces of such implants, which leads to the previously-mentioned binding tissue layer. Accordingly such implants are not anchored firmly in the bone, and they are rather capable of carrying out at least small movement relative to the jaw bone, which is spring-cushioned by the fringe of soft tissue.
Secondly, only metal parts have been provided on such implants in the area thereof extending through the mucous membrane. Moreover, the mucous membrane tissue only conditionally contacts in a bacteria-tight manner on such metal parts. This is related to the fact that even highly corrosion resistant metals, such as, titanium, tantalum or niobium, even in the case of only slight damage of the surface, as might occur again and again during chewing as a result of food components sliding down, release metal ions to the surroundings. The corrosion resistance of these metals in the body medium is due to the formation of dense oxide layers on the surface, which sufficiently avoids the start of dissolution of the very base metals themselves, but only as long as such oxide layers remain undamaged. The metal ions which temporarily start to dissolve after damage to these oxide layers influence the activity of the cells in the immediate surroundings. This leads to irritation of the tissue in the area of the highly sensitive ends of mucous membrane, which upon addition of more unfavorable effects may lead to a penetration by and growth of the bacteria in the depth of the gingiva propria or the epithelium of the gingiva propria. This in turn has, as a consequence, a formation of pockets of soft tissue of fairly large size around the neck of the implant.
The shaking amplitude of the implants which, as mentioned above, are merely surrounded by a soft binding tissue, must be considered as a very important factor which considerably magnifies such irritation of the mucous membrane tissue in the neck area. Since such implants are not firmly anchored in the bone, they carry out separate movement relative to the jaw in their soft tissue bed, for example, in the case of the loads occurring during chewing and above all also during the loads caused by the tongue, which are brought about by the act of swallowing, as a result of which the end of the mucous membrane is subjected to loads or pressure in a completely unphysiological manner.
Beyond that, leaf implants of the previously-used form have a part on the post-shaped part, projecting into the mouth cavity for the attachment of a bridge or superstructure, which extends way above the mucous membrane level. The consequence of this is that such leaf implants cannot be sufficiently protected against loads during the healing-in phase. Such loads during the healing-in phase however, promote the development of the soft tissue fringe, which has been mentioned above.